A ligand binding assay is an analytical technique for measuring concentrations of substances that react selectively with specific binding proteins. Such substances are called ligands in the field of Biochemistry. Immunoassays to measure concentrations of antigens that react selectively with specific antibodies comprise a class of ligand binding assays.
Assay reagents in a ligand binding assay generally include:
1. A specific binding protein such as an antibody that specifically and strongly binds the substance to be measured, referred to as the analyte, the strong binding being characterized by an equilibrium dissociation constant less than about 10.sup.-8 M; and
2. Labeled analyte.
The label provides a measurable property of the system for the purpose of monitoring the extent of binding of labeled analyte to antibody in a solution.
Fluorescent dyes have been shown to be useful as labels in homogeneous immunoassays as described in co-pending Application Ser. No. 518,965.
That application discloses a method and composition, using a nonprotein solute, for preferentially altering the relative intensities of bound and free dye labels. The method and composition make use of the present inventor's discovery that certain surfactants operate to effect differential fluorescence between bound and free labelled analyte. It would be desirable, however, to be able to characterize more precisely the surfactant-dye-analyte relationship that gives rise to differential fluorescence useful for ligand binding assays.